Bird deaths continue at a large solar plant nearing completion in the Mojave Desert, and biologists are unable to account for the whereabouts of 23 of the federally Threatened desert tortoises displaced by the project. That's according to a monthly report filed by project owner BrightSource Energy with the California Energy Commission (CEC).

According to the Ivanpah Solar Electric Generating System's Monthly Compliance Report for December 2013, project biologists reported 13 dead birds found on a portion of the nearly 4,000-acre project in December. That figure is about the same as November's tally of 11, and down significantly from the site's October death toll of 52 birds and six bats, suggesting that bird deaths at the site may spike during seasonal bird migration. Causes of death included collisions with mirrors and burn injuries from solar flux.

Meanwhile, the compliance document also reports that the whereabouts are unknown of 23 of the Threatened desert tortoises project biologists have been monitoring, including five sub-adult tortoises that have been missing from the project's tortoise holding pens for 18 months or more.

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The Ivanpah project is expected to start delivering up to 377 megawatts of power to California's grid early this year.

The five tortoises missing from the project's holding pens had not been seen by project biologists for at least 12 months as of the end of November, said the report, cautioning that "Juvenile tortoises in the holding pens are... difficult to locate due to their small size and cryptic nature and often reappear after several months of being unaccounted for."

Several months is one thing: close to three years is another. According to data in the document contained only in a legend on a map and not searchable as text, a tortoise called BS 54 was last seen in the pens in March 2011.

Then its colleague BS 301 was last seen six months later, in September 2011; tortoises BS 98, BS 200, and BS 211 were last reported in May 2012. That's 18 months before November 2013, which technically speaking is indeed "at least 12 months."

The report also notes that ravens have been observed "regularly perching around the quarantine pens, including on the netting above the pens." Predation by ravens is a main cause of death of juvenile and subadult tortoises. As of December, at least, the netting and fencing are reported to be sufficiently intact to keep ravens out.

The five tortoises missing for a year from the tortoise pens leave 102 sub-adult torts in the pens whose whereabouts are still known. The other 18 missing tortoises are part of the group that was released to a relocation area, after having radio transmitters affixed so that biologists could monitor their movements and their survival. Those tortoises may not all actually be missing: there's a chance that some of the transmitters are malfunctioning due to battery failure, or that some of the tortoises may have wandered out of range.

Of those tortoises, at least six went missing this year according to spreadsheets included in the December compliance document. Three of the tortoises that went missing this year were last detected in August. Eight of the tortoises were missing all year. Six tortoises missing this year and eight missing since last year adds up to 14 tortoises missing in December, a discrepancy from BrightSource's reported 18 missing non-penned tortoises that was not immediately explained by the document. Of all the tortoises marked as missing in the spreadsheet, one turned up again a month after she was marked AWOL.

Desert tortoises are listed as Threatened under the federal Endangered Species Act. BrightSource's project ran into a tortoise speedbump in 2011, when project workers started finding hundreds more of the Threatened reptile than its biologists had anticipated.

"Biologists will continue to listen for radio signals for the missing tortoises with transmitters and will look for them in the field when conducting scheduled surveys and monitoring," reports BightSource in its compliance document. "Husbandry personnel will
continue to search for the missing juvenile tortoises in the holding pens."

If BrightSource personnel do find the missing juveniles alive and well in their pens after not finding them in those pens for up to three years, we will report on that happy fact here.

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